Method of building up pitted holes in a metal sheet



June 14, 1938. I J, McKE RIHAN I 4 2,120,525

METHOD OF BUILDING UP FITTED HOLES IN A METAL SHEET Filed Jun 1, 1957FIG: I FIGHZIZI 113 L6 1 1B 5 Z WITNESSES: I I N V EN TOR:

I Thomas J M Kerihan,

Patented June 14, 1938 UNITED STATES PATENT OFFICE METHOD OF BUILDING UPPITTED' HOLES IN A METAL SHEET My invention relates generally to thebuilding up of corroded or worn metals and more particularly to a methodof building up pitted holes in a metal sheet.

Becoming more specific my invention is immediately concerned withbuilding up pitted holes in the crown sheet of a boiler in which thewelding is done from the fire side of the sheet. In crown sheet boilers,where crown stays are used to support the pressure load, the part of thecrown sheet surrounding the crown stay is subject to grooving action,which thins the sheet to the extent that the crown sheet, as a whole orin part, has to be renewed. Much difficulty is experienced in buildingup pitted holes by welding when the work is done from the water side ofthe boiler because of the cramped and obscured working space. Inattempting to build up from the water side of the boiler sheet, longelectrodes to reach the pitted parent metal are necessary for theautogenous or self-produced welding process and this has provedunsatisfactory for the operators vision is seriously obstructed. Workdone in this manner has a rough corrugated surface which cannot bedressed smooth in order to prevent the accumulation of sediment.

Therefore the principal object of my invention is to provide a method ofbuilding up pitted holes in the crown sheet of a boiler by which thewelding and other operations can be done from the fire side of thesheet. Another object is to provide a method for the rebuilding of anycorroded sheet from the side opposite the corroded surface. Furtheradvantages will become apparent from the following description of apreferred form of my invention, reference being had to the accompanyingdrawing.

Fig. I of the drawing shows a vertical section of a portion of the crownsheet of a boiler which has been pitted around a crown stay on the waterside, the crown stay not being shown.

Fig. II shows a plan View of the same. Fig. III shows a verticalsectional view of the same after the corroded area on the water side ofthe crown sheet has been pressed into a smooth surface from the fireside.

Fig. IV is a vertical section of the same showing a building up by theaddition of metal from the fire side.

Fig. V is a plan view from the fire side of the sheet showing the builtup metal of Fig. IV; and, Fig. VI is a vertical section showing thebuilt up crown sheet after the hole for the crown stay has beenre-drilled and the excess building up metal smoothed off on the fireside of the crown sheet.

In the preferred practice of my method of building up a corroded area onthe water side of the crown sheet of a boiler, I first heat the 5 parentmetal in the corroded area 3 and then apply a backing element I againstthe water side A of the crown sheet 2, the crown stay having first beenremoved fromthe crown stay hole 5. This backing means I may be of anycon- 10 venient form which can be easily positioned in the restrictedarea inside of a boiler. The backing means I should extend over a pittedarea 3 in the water side A of the crown sheet 2 to be built up and mustbe securely positioned and 15 heavy enough to resist a pressure forcingout the pitted area 3 against the backing means I.

I then apply pressure to the fire side B of the crown sheet 2 until thecorroded area 3 is forced out into a smooth surface on the water side A20 against the backing means I, as shown in Fig. III, leaving adepression 6 on the fire side B. Any convenient pressure means may beused; I have used with success a pneumatic hammer of a well-known type.The next step is the build- 25 ing up of the depression 6 on the fireside B of the crown sheet 2 caused by forcing out the corroded area 3against the backing means I. I use autogenous welding to build up thisdepression 6 from the fire side B, but other suitable 30 types ofwelding could be used, if desirable. Fig. IV shows welding material 1after the aforesaid depressed area 6 has been built up by welding. Thewelding material 1 is distributed generously with a view to a finalgrinding and boring of 35 the hole 5. I then re-drill the hole 5 for thecrown stay and grind off the excess of the welding material 1 on thefire side B. The finished product is shown in Fig. VI, ready to bere-tapped and to then receive the crown stay in re-assem- 0 bling forfurther use. The smooth surface on the water side A is substantially asgood as the original surface.

Thus my invention provides a simple and practical method of building upthe corroded area shown in Fig. I by working from the fire side Binstead of the water side A which is so cramped and inaccessible. I havefound that my method of repairing crown sheets has greatly reduced 50the difficulty of building up these pitted areas and made it possible torepair corrosion in much less time than formerly was needed. Thefinished product is also much better than the results previouslyobtained by working from the water 55 10 said pitted area, applyingpressure rigidly over the area of said sheet opposite the pitted side,pressing said pitted area outwardly against the backing means until asmooth surface is obtained on the previously pitted side, building up byautogenous welding the depressions caused by said application ofpressure to the side opposite to the pitted area of said sheet, removingthe excess Welding material, and redrilling a hole for the crown bolt.

THOMAS J. McKERIHAN.

